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Presistent CSMA : Presistent CSMA :  If station has data  sense the line  The line busy  station wait for a several time  The line empty  send the frame  If Collision occurred  station wait for a few time then try to re-send  Call 1 presistent because the probability of transmit = 1, if the line is empty. Presistent : ALWAYS detect the line until really empty Presistent : ALWAYS detect the line until really empty Persistent and Nonpersistent CSMA

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Comparison of the channel utilization versus load for various random access protocols.

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The possibility collision occure:  Station detect the line ‘ empty ‘ but maybe the packet just sent from another station not yet arrive. This because of the delay propagation.  2 stations at the same time wait the line which has been used by the another station. If the transmission just finish then the both stations together send the packet and access the line.   COLLISION!!

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Packet Time delay : The Duration time between packet sent by the sender until ALL packets receive by the receiver.  very important The Duration time between packet sent by the sender until ALL packets receive by the receiver.  very important

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CSMA with Collision Detection CSMA/CD can be in one of three states: contention, transmission, or idle.

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 At CSMA/CD probably will collide in the interval “ Contention”  If  ( length of line) large and frame is short – the critical time (contention) more longer  handle by Bit map Protocol Collision-Free Protocols

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At the Collision Free Protocol :  Access to the channel by the Station, same as a sequence of the bit map  Every stasion has the unique allocation time for access the line and cannot use by another stasion.  If the stasion not ready when their turn comes up, they must wait their turn in the next period.

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Binary Count Down The overhead of the protocol = 1 bit per station. That will develop by using the same length of address and broadcasting to the network. Every position of bit from the different station must OR and called Binary Count Down. How to Compare is as: Example : 0010,0100,1001,1010

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 Containing a high speed back plane and room for typlcally 4 – 32 plug-in line card, each containing 1 to 8 connector. Most Often each connector has a 10 Base=T twist pair connection to a single host computer.  Each card forms its own collision domain independent of the other Switched Ethernet

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 Development of Ethernet by increasing thespeed, using more than 10 Mbps. Using Fiber Cabel  One was called FDDI ( Fiber Distributed Data Interchange or Fiber Channel  Must be compatible with Classic Ethernet Fast Ethernet

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 To connect LAN-LAN  On the Data Link Layer  Usually for 802 LAN  Only discuss Bridge  The reason why an organization using several LAN 1. Different needs of many Universities / 1. Different needs of many Universities / Departements  Several LAN need bridge Departements  Several LAN need bridge BRIDGE

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2. The different geographies – many building in the separate area building in the separate area 3. Overload - thousands workstation - Need to divided into several LAN - Need to divided into several LAN - Need Bridge - Need Bridge 4.The distance between machines too far (mis > 2,5 km) (mis > 2,5 km)  Using the single cable – the round trip delay is large  Need divided into several LAN  Need bridge

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5. Bridge can select which is continue or not  using programming  not only copy  Repeater 6.Bridge support security to the organization

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Another Problems :  ke : no problem  ke : there are 2 problems : has preority, does not has priority  ignored –802.4 has 1 bit in the header as sender, token ack from destination.  to also has problem as above

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Bridges from 802.x to 802.y Operation of a LAN bridge from to

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Bridges from 802.x to 802.y (2) The IEEE 802 frame formats. The drawing is not to scale.

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Local Internetworking A configuration with four LANs and two bridges.

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TRANSPARENT BRIDGE  Every things are transparent  Just plug between networks without any changes at all  the system will run  Works as, ‘promises mode’, receive every frame, send to many LAN and many direction  Bridge works depend on address table in the bridge to find which frame discard or not.

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 Routing procedure depend on sender and frame’s receiver  a)If receiver and sender comes from the same LAN  frame will be discard b) If receiver and sender comes from the different LAN  frame will be pass c)If receiver and sender not clear and unknown  using flooding  Flooding : sometimes create the trouble  because they must copy every frame Handle by  Spanning Tree Bridge

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Spanning Tree Bridges Two parallel transparent bridges.

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Spanning Tree Bridges (2) (a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree.

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Remote Bridges Remote bridges can be used to interconnect distant LANs.

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Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers.

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Virtual LANs A building with centralized wiring using hubs and a switch.

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Virtual LANs (2) (a) Four physical LANs organized into two VLANs, (a) Four physical LANs organized into two VLANs, gray and white, by two bridges. gray and white, by two bridges. (b) The same 15 machines organized into two (b) The same 15 machines organized into two VLANs by switches. VLANs by switches.

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The IEEE 802.1Q Standard Transition from legacy Ethernet to VLAN-aware Ethernet. The shaded symbols are VLAN aware. The empty ones are not.